Your student can save her project as CS5 using CS5.5. Just go to File > Save As and change the save as type from Flash CS5.5 to Flash CS5. Please note that any CS5.5 feature used in that fla will not be saved when save as CS5.
Flash Authoring, QA
I've forwarded your reply to the student.
So, just a quick follow-up.
If the student is using tools that are common to both CS5.5 and CS5 workspace's that's ok. And, if the student imported Photoshop files (with or without layers) and created graphic symbols or button symbols in CS5.5, the graphics and symbols should be in the library and/or on the stage after they saved and opened as a CS5 document.
Can you give me an example of a feature that would not be available?
Yes, the examples you listed should be okay. Some new CS5.5 features that are not supported in CS5 are rendered symbol as bitmap/export as bitmap, IK pinning, etc...
You can find a more complete list here: